It Takes 20 Seconds Before People Get Annoyed About Waiting for the Elevator

Theresa Christy, a mathematician who works for Otis Elevator Co (they probably power your building), told the WSJ that once you press a button and wait for the elevator, it takes about 20 seconds before you start getting impatient and annoyed.

Is that it? Or is that on the long side? If I imagine a 20-second count in my head, it seems on the long side. But if I can see the elevator light up the floors, maybe it's not so long. What do you guys think?

Christy actually revealed a lot of interesting tidbits about elevators and how they work and solve problems with math. Like how to tweak elevator speed to accomodate more rides, how many people squeeze into elevators in Western Countries versus Asia and how she uses a computer simulation program that replays elevator decision making (like a video game!) to analyze what to do. More here.